19j should surely go faster than 50!

problem solved 200tdi goin in

does your fuel tank pressurise, check your turbo boost diaphram on the side of the injector pump, pull the pipe of and blow, if you hear air bubbling in the tank its split, they are about £20 new. bob....

Don't forget the magic words "200tdi" don't guarantee an improvement, you could have the same problems with a 25 year old engine as you have now.
Hear it running before you buy.
No power could be a simple leak or adjustment on any turbo engine, my pajero did what yours does and it was a loose jubilee clip!